Integrated magnetoresitive speed and direction sensor

Abstract

An integrated circuit magnetoresistive speed and direction sensor generally utilizes an AMR bridge circuit thereby allowing for increased air gap performance as compared to conventional Hall-effect element based sensors. The AMR sensor is capable of sensing ring magnets or bar magnets magnetized with one or more magnet poles along the desired travel. The number of poles of the magnet should be optimized based upon the application design. In order to obtain speed and direction information, two bridge circuits can be placed within proximity (I.e., the exact location and shape of the bridge can be determined based upon the target and desired performance) of each other. The signals of the two bridge circuits can be compared on integrated electronics. The bridges are generally rotated 45 degrees to reduce and/or eliminate offsets, which provide the sensor with a large air gap performance.

1 . A sensor system, comprising: 
 a first magnetoresistive bridge circuit placed in proximity to and spatially separated from a second magnetoresistive bridge circuit, wherein said first and second magnetoresistive bridge circuits are located on an integrated circuit; and    a magnetic target magnetized with a plurality of magnet poles along a desired path of travel, wherein said first and second magnetoresistive bridge circuits are located in proximity to said magnetic target, such that said first magnetoresistive bridge circuit generates a first signal and said second magnetoresistive bridge circuit generates a second signal, wherein said first and second signals are compared to one another and utilized to determine a speed and direction of said magnetic target and wherein said first and second magnetoresistive bridge circuits provide a magnetic sensitiviy that is approximately constant over an operating temperature thereof.    
   
   
       2 . The system of  claim 1  wherein said first and second magnetoresistive bridge circuits are located on said integrated circuit wherein said integrated circuit provides a speed pin and a direction pin, such that a frequency of an output and a digital output state of said direction pin indicates a direction of rotation of said ring magnet, wherein said direction of said ring magnet is determined from a phase difference between said first and second magnetoresistive bridge circuits.  
   
   
       3 . (canceled)  
   
   
       4 . The system of  claim 1  further comprising a four terminal device comprising said first and second magnetoresistive bridge circuits, wherein said four terminal device comprises a power connection, a ground connection and first and second outputs, wherein said first and second outputs respectively provide speed and direction data, which provides data Indicative of said speed and direction of said magnetic target.  
   
   
       5 . The system of  claim 4  wherein said first output provides speed data in a form of a square wave signal with each period thereof corresponding to one pole of said magnetic target.  
   
   
       6 . The system of  claim 5  wherein said second output provides direction data in a digital state, which indicates a rotational direction of said magnetic target.  
   
   
       7 . (canceled)  
   
   
       8 . The system of  claim 1  wherein said magnetic target comprises a ring magnet.  
   
   
       9 . (canceled)  
   
   
       10 . A sensor system, comprising: 
 a first bridge circuit placed in proximity to and spatially separated from a second bridge circuit, wherein said first and second bridge circuits are located on an integrated circuit (IC), and wherein said first bridge circuit comprises a magnetoresistive (MR) circuit and wherein said second bridge circuit comprises a magnetoresistive (MR) circuit;    a magnetic target magnetized with a plurality of magnet poles along a desired path of travel, wherein said first and second bridge circuits are located in proximity to said magnetic target, such that said first bridge circuit generates a first signal and said second bridge circuit generates a second signal, wherein said first and second signals are compared to one another and utilized to determine a speed and direction of said magnetic target;    wherein said integrated circuit comprises a four terminal device comprising said first and second bridge circuits, wherein said four terminal device comprises a power connection, a ground connection and first and second outputs, wherein said first and second outputs respectively provide speed and direction data, which provides data indicative of said speed and direction of said magnetic target; and    wherein said first output provides speed data in a form of a square wave signal with each period thereof corresponding to one pole of said magnetic target and wherein said second output provides direction data in a digital state, which indicates a rotational direction of said magnetic target and wherein said first and second MR bridge circuits provide a magnetic sensitivity that is approximately constant over an operating temperature range thereof.    
   
   
       11 . (canceled)  
   
   
       12 . (canceled)  
   
   
       13 . (canceled)  
   
   
       14 . A sensor method, comprising the steps of: 
 locating a first magnetoresistive bridge circuit placed in proximity to and spatially separated from a second magnetoresistive bridge circuit; and    providing a magnetic target magnetized with a plurality of magnet poles along a desired path of travel, wherein said first and second magnetoresistive bridge circuits are located in proximity to said magnetic target, such that said first magnetoresistive bridge circuit generates a first signal and said second magnetoresistive bridge circuit generates a second signal, wherein said first and second signals are compared to one another and utilized to determine a speed and direction of said magnetic target wherein said first and second magnetoresistive bridge circuits provide a magnetic sensitivity that is approximately constant over an operating temperature thereof.    
   
   
       15 . The method of  claim 14  further comprising the step of configuring said first and second bridge circuits on an integrated circuit (IC).  
   
   
       16 . (canceled)  
   
   
       17 . The method of  claim 14  further comprising the step of: 
 providing a four terminal device comprising said first and second bridge circuits, wherein said four terminal device comprises a power connection, a ground connection and first and second outputs, wherein said first and second outputs respectively provide speed and direction data, which provides data Indicative of said speed and direction of said magnetic target.    
   
   
       18 . The method of  claim 17  further comprising the steps of: 
 generating speed data from said first output in a form of a square wave signal with each period thereof corresponding to one pole of said magnetic target;    generating direction data In a digital state from said second output to provide an indication of a rotational direction of said magnetic target; and    wherein said first and second bridge circuits provide a magnetic sensitivity that is approximately constant over an operating temperature range thereof.    
   
   
       19 . The method of  claim 18  further comprising the step of configuring said magnetic target to comprise a ring magnet.  
   
   
       20 . The method of  claim 18  further comprising the step of configuring said magnetic target to comprise a bar magnet.